Golf club head

ABSTRACT

Provided is a golf club head that includes a face portion for hitting a ball. The face portion has a thick portion that includes a face center, and a peripheral portion that is thinner than the thick portion and surrounds the thick portion. The thick portion extends along a central axis line, and has a recessed portion on at least one side of the central axis line so that a central region of the thick portion along the central axis line is recessed more toward the central axis line than parts of the thick portion on two sides of the central region along the central axis line. Note that the central axis line extends in a top-sole direction or in a direction inclined from a toe side toward a heel side along a direction from a sole side toward a top side.

CROSS REFERENCE TO RELATED APPLICATION

This application claims a priority to Japanese Patent Application No.2015-113364 filed on Jun. 3, 2015, which is hereby incorporated byreference in its entirety.

FIELD OF INVENTION

The present invention relates to a golf club head.

BACKGROUND

Conventionally, various innovations have been made with respect to thedesign of the thickness of the face portion of a golf club head from theviewpoint of strength, the viewpoint of extending the flight-distance,and the like. In general, from the viewpoint of ensuring strength, itcan be said that a thicker face portion is better, but from theviewpoint of extending the flight-distance, it is important to reducethe thickness of the face portion to improve the restitutionperformance. JP 2010-530783A discloses a golf club head in which thecentral region of the face portion, which normally receives the mostimpact when hitting a ball, is formed with a high thickness, and theperipheral region thereof is formed with a low thickness. In this golfclub head, the thick portion in the central region is formed with anapproximately elliptical shape.

SUMMARY of INVENTION

Incidentally, improvement in flight-distance is a never-ending goal forgolfers. On the other hand, it is also necessary to ensure strength forthe golf club head. In view of this, the inventor of the presentinvention sought a method for further improving flight-distance whilealso ensuring strength for the golf club head through an innovation inthe thickness design.

An object of the present invention is to provide a golf club head thatcan extend the flight-distance while also ensuring strength.

A golf club head according to a first aspect of the present invention isa golf club head that includes a face portion for hitting a ball. Theface portion has a thick portion that includes a face center, and aperipheral portion that is thinner than the thick portion and surroundsthe thick portion. The thick portion extends along a central axis line,and has a recessed portion on at least one side of the central axis lineso that a central region of the thick portion along the central axisline is recessed more toward the central axis line than parts of thethick portion on two sides of the central region along the central axisline. Note that the central axis line extends in a top-sole direction orin a direction inclined from a toe side toward a heel side along adirection from a sole side toward a top side.

A golf club head according to a second aspect of the present inventionis the golf club head according to the first aspect, wherein the thickportion has the recessed portion on each side of the central axis line.

A golf club head according to a third aspect of the present invention isthe golf club head according to the second aspect, wherein the recessedportions on both sides of the central axis line oppose each other acrossthe central axis line.

A golf club head according to a fourth aspect of the present inventionis the golf club head according to any of the first to third aspects,wherein the central axis line is a line segment having a maximum lengthamong line segments that pass through a centroid of the thick portionand are overlapped with the thick portion, and intersects a boundaryline of the thick portion at a first intersection and a secondintersection. The face portion includes a hit point distribution region.The hit point distribution region is surrounded by a first orthogonalline that passes through the first intersection and is orthogonal to thecentral axis line, a second orthogonal line that passes through thesecond intersection and is orthogonal to the central axis line, and aboundary line of the face portion. A groove that extends along theboundary line of the face portion and is at least partially overlappedwith the hit point distribution region is formed on a back surface sideof the face portion.

A golf club head according to a fifth aspect of the present invention isthe golf club head according to the fourth aspect, wherein the boundaryline of the face portion includes a top line on a top side that extendsbetween a toe-side end point, being a point farthest on a toe side, anda heel-side end point, being a point farthest on a heel side, andincludes a sole line on a sole side that extends between the toe-sideend point and the heel-side end point. The hit point distribution regionhas a first corner point on a toe side and a second corner point on aheel side on the top line, and has a third corner point on a toe sideand a fourth corner point on a heel side on the sole line. The grooveincludes at least one of a toe-side groove and a heel-side groove. Thetoe-side groove extends at least from the first corner point into thehit point distribution region along the boundary line of the faceportion but does not reach the second corner point, and the heel-sidegroove extends at least from the fourth corner point into the hit pointdistribution region along the boundary line of the face portion but doesnot reach the third corner point.

A golf club head according to a sixth aspect of the present invention isthe golf club head according to the fifth aspect, wherein the grooveincludes both the toe-side groove and the heel-side groove.

A golf club head according to a seventh aspect of the present inventionis the golf club head according to the fifth aspect or the sixth aspect,having a volume of 400 cubic centimeters or more.

A golf club head according to an eighth aspect of the present inventionis the golf club head according to the fourth aspect, wherein theboundary line of the face portion includes a sole line on a sole sidethat extends between a toe-side end point, being a point farthest on atoe side, and a heel-side end point, being a point farthest on a heelside. The groove extends along the sole line.

A golf club head according to a ninth aspect of the present invention isthe golf club head according to the eighth aspect, having a volume lessthan 400 cubic centimeters.

Generally, hit points on a face portion are distributed around astraight line (referred to hereinafter as the actual hit pointdistribution line) that passes through the face center region and isinclined from the heel side toward the toe side along the direction fromthe sole side toward the top side. On the other hand, the face portionof the golf club head according to the present invention is providedwith a thick portion that includes the face center and extends along acentral axis line that intersects the actual hit point distributionline. Accordingly, the face center region is thick, thus ensuringstrength. Also, the thick portion is provided with a recessed portion onat least one side of the central axis line so that the central region ofthe thick portion along the central axis line recedes more toward thecentral axis line than the parts of the thick portion on the two sidesof the central region along the central axis line. In other words, thethick portion is recessed in the direction in which the actual hit pointdistribution line extends, and thus the thin region spreads out so as toconform to the actual hit point distribution line. As a result, the highrestitution factor area spreads out along the actual hit pointdistribution region, and it is possible to improve the flight-distance.Accordingly, it is possible to extend the flight-distance while alsoensuring strength for the golf club head.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view of a golf club head according to a firstembodiment in a reference state;

FIG. 2 is a plan view of the golf club head in the reference state;

FIG. 3 is a cross-sectional view taken along line A-A in FIG. 2;

FIG. 4 is a front view of the golf club head in the reference state;

FIG. 5 is a front view of a face portion of a golf club head accordingto a second embodiment in a reference state;

FIG. 6 is a front view of a face portion of a golf club head accordingto a variation in the reference state;

FIG. 7 is a front view of a face portion of a golf club head accordingto another variation in the reference state; and

FIG. 8 is a front view of the golf club head according to the firstembodiment in the reference state, and shows an actual hit pointdistribution region.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Golf club heads according to several embodiments of the presentinvention will be described below with reference to the drawings.

1. First Embodiment

1-1. Overview of Golf Club Head

FIG. 1 is a perspective view of a golf club head (hereinafter sometimessimply referred to as the “head”) 100 of the present embodiment in areference state, and FIG. 2 is a plan view of the head 100 in thereference state. The reference state of the golf club head will bedescribed later. The head 100 is a hollow structure and has wallsurfaces formed by a face member 1, a crown portion 2, a sole portion 3,a side portion 4, and a hosel portion 5. The head 100 of the presentembodiment is a driver (#1).

The face member 1 constitutes a front portion of the head 100 thatserves as the surface for hitting a ball. The crown portion 2 isadjacent to the face member 1 and constitutes the upper surface of thehead 100. The sole portion 3 constitutes the bottom surface of the head100, and is adjacent to the face member 1 and the side portion 4. Also,the side portion 4 is the portion between the crown portion 2 and thesole portion 3, and extends from the toe side of the face member 1,across the back side of the head 100, to the heel side of the facemember 1. Furthermore, the hosel portion 5 is the portion providedadjacent to the heel side of the crown portion 2, and has an insertionhole 51 for the insertion of the shaft (not shown) of the golf club. Acentral axis Z of the insertion hole 51 conforms to the axis of theshaft.

The following describes the aforementioned reference state. As shown inFIGS. 1 and 2, the reference state is defined as a state in which thecentral axis Z is in a plane (hereinafter, the reference vertical plane)P that is perpendicular to a horizontal plane H (see FIG. 3), andfurthermore the head is placed on the horizontal plane H at apredetermined lie angle and real loft angle. Also, as shown in FIG. 2,the direction of the line of intersection of the reference verticalplane P and the horizontal plane H will be referred to as the toe-heeldirection, and the direction that is perpendicular to the toe-heeldirection and parallel to the horizontal plane H will be referred to asthe face-back direction. Also, the direction perpendicular to thehorizontal plane H will be referred to as the top-sole direction. Notethat in the description of the present embodiment, unless otherwisestated, “forward-rear” means the face-back direction, the “face side” isforward, and the “back side” is rearward. Also, unless otherwise stated,“up-down” refers to the top-sole direction, the “top side” is upward,and the “sole side” is downward.

The head 100 can be formed from a titanium alloy having a specificgravity of approximately 4.4 to 5.0 (e.g., Ti-6Al-4V), for example.Besides a titanium alloy, the head can be formed from one or two or morematerials selected from among stainless steel, maraging steel, analuminum alloy, a magnesium alloy, an amorphous alloy, and the like.Also, there is no limitation to a metal material, and the head can alsobe formed using a fiber-reinforced plastic or the like. Moreover, it ispreferable that the volume of the head 100, which is a driver, is 400cubic centimeters or more.

The head 100 of the present embodiment is constituted by assembling theface member 1 with a head body 6 that is a hollow structure having thecrown portion 2, the sole portion 3, the side portion 4, and the hoselportion 5. The head body 6 and the face member 1 are joined by welding(TIG (Tungsten-Inactive Gas) welding, plasma welding, laser welding,brazing, etc.), for example. The head body 6 has an opening on the frontside surrounded by the crown portion 2, the sole portion 3, and the sideportion 4, and the face member 1 is attached so as to block thisopening. The head body 6 can also be an assembly of multiple parts, andcan also be formed as a single body. The head body 6 and the face member1 can be produced using various methods. For example, the head body 6can be manufactured by casting using a known lost-wax precision castingmethod or the like. Also, the face member 1 can be manufactured using aforging method, flat plate press machining, casting, or the like. Notethat the component configuration of the head 100 described here is anillustrative example, and it can also be an assembly of multiplecomponents different from this example, and can also be formed as asingle body.

Hereinafter, the face member 1 will be described with reference to FIG.3 as well. FIG. 3 is a cross-sectional view taken along line A-A in FIG.2. As shown in FIGS. 1 to 3, the face member 1 of the present embodimentis of the so-called “cup face” type. In other words, the face member 1is shaped as a cup that has a flat plate-shaped face portion 11 forhitting a ball and a rising portion (extending portion) 12 that extendsrearward from the peripheral edge of the face portion 11.

This cup face-type face member 1 has a higher restitution factor in theface portion 11 than a face member not having a rising portion, becausethe area of flexure is larger by an amount corresponding to the risingportion 12. Also, in the case where the cup face construction isemployed, the connection portion of the face member 1 and the head body6, where rigidity tends to increase, moves rearward of the face portion11, and therefore the overall face portion 11 flexes easily.Accordingly, the cup face construction contributes to an increase inflight-distance.

Additionally, various innovations have been made to the golf club head100 in order to improve the restitution factor of the face portion 11for the purpose of increasing the flight-distance. Specifically, acharacteristic structure has been formed in the vicinity of theconnection portion of the face member 1 and the head body 6, and aninnovation has also been made to the thickness structure of the crownportion 2 and the face portion 11. These features will be describedbelow in order.

1-2. Structure in Vicinity of Connection Portion of Face Member and HeadBody

As shown in FIGS. 1 and 2, a front edge portion 20 of the crown portion2 has a protruding shape in which a central region thereof projectsforward. Specifically, the front edge portion 20 of the crown portion 2has a first toe-side portion 20 a that is on the toe side, a firstheel-side portion 20 b that is on the heel side, and a first centralportion 20 c located between the portions 20 a and 20 b, and the firstcentral portion 20 c projects forward more than the first toe-sideportion 20 a and the first heel-side portion 20 b. On the other hand, inthe rising portion 12 of the face member 1, the portion fixed to thefront edge portion 20 of the crown portion 2 (hereinafter, the fixedportion being referred to as the “upper rising portion 30”) has astructure that corresponds to the above-described structure of the crownportion 2. Specifically, in the upper rising portion 30, the two sideregions have a protruding shape of projecting rearward, and the centralregion has a receding shape of being recessed forward. Specifically, theupper rising portion 30 has a second toe-side portion 30 a that isjoined to the first toe-side portion 20 a, a second heel-side portion 30b that is joined to the first heel-side portion 20 b, and a secondcentral portion 30 c that is joined to the first central portion 20 c.Also, the second toe-side portion 30 a and the second heel-side portion30 b project rearward more than the second central portion 30 c. Notethat the second central portion 30 c is the portion located between thesecond toe-side portion 30 a and the second heel-side portion 30 b.

The protruding shape of the front edge portion 20 of the crown portion 2and the protruding shape of the upper rising portion 30 of the facemember 1 contribute to an enlargement of the high restitution area onthe face portion 11. Specifically, the connection portion of the facemember 1 and the head body 6 recedes rearward on the toe side and theheel side, and thus the amount of flexure during ball-hitting increasesin the toe-side and heel-side portions of the face portion 11, andtherefore the restitution factor improves in the face portion 11overall.

1-3. Thickness Structure of Face Portion

Next, the thickness structure of the face portion 11 that contributes toan increase in the flight-distance will be described. The front surface(hereinafter, called the face surface) side of the face portion 11 thatserves as the ball hitting face is formed so as to be smooth and flat.On the other hand, unevenness is formed on the back surface side of theface portion 11. In other words, the face portion 11 is constituted bymultiple regions having different thicknesses.

FIG. 4 is a front view of the head 100 in the reference state.Accordingly, it would not actually be possible to see the thicknessstructure formed on the inner surface of the face portion 11 in thisfigure. However, in consideration of facilitating understanding, thethickness structure is shown in the figure. As shown in FIG. 4, a thickportion 50 is formed in the central region of the face portion 11, and aperipheral portion 60 that is thinner than the thick portion 50 isformed so as to surround the thick portion 50. The peripheral portion 60has an approximately ring-shaped transition portion 61 that surroundsthe thick portion 50 and comes into contact with the thick portion 50,and thin portions 62 a and 62 b that further surround the transitionportion 61 and come into contact with the transition portion 61. Thetransition portion 61 is thicker than the thin portions 62 a and 62 b,but is thinner than the thick portion 50. The thin portions 62 a and 62b are separated on the toe side and the heel side respectively, with thetransition portion 61 therebetween, the thin portion 62 a is the regionon the heel side of the transition portion 61, and the thin portion 62 bis the region on the toe side of the transition portion 61. In thepresent embodiment, the transition portion 61 is constituted so as togradually decrease in thickness from the thick portion 50 toward theoutside, that is to say toward the thin portions 62 a and 62 b, and thischange in thickness is continuous. However, the thicknesses of thetransition portion 61 may be constant, and even in the case of changing,the thicknesses may change in a non-continuous manner, such as in astepwise manner.

As shown in FIG. 3, in the present embodiment, a thickness w1 of thethick portion 50 is approximately constant and can be preferably set to2.0 mm≦w1≦4.5 mm or more preferably 3.0 mm≦w1≦4.0 mm, and in the presentembodiment, w1=3.65 mm. Also, in the present embodiment, a thickness w2of the thin portions 62 a and 62 b is also approximately constant andcan be preferably set to 1.5 mm≦w2≦3.0 mm or more preferably 1.8mm≦w2≦2.6 mm, and in the present embodiment, w2=2.00 mm.

Hereinafter, for the sake of convenience in the description, assumingthat the head 100 is placed in the reference state, a point Pt fartheston the toe side on the peripheral edge of the face portion 11 (theboundary line between the face portion 11 and the rising portion 12)will be referred to as the toe-side end point, and a point Ph fartheston the heel side will be referred to as the heel-side end point. Also,on the peripheral edge of the face portion 11, the top-side lineextending from the toe-side end point Pt to the heel-side end point Phwill be referred to as a top line L1, and a sole-side line extendingfrom the toe-side end point Pt to the heel-side end point Ph will bereferred to as a sole line L2. Furthermore, a central axis line L3 isdefined that is inclined from the toe side to the heel side along thedirection from the sole side to the top side on the face surface. In thepresent embodiment, the central axis line L3 is the line segment thatpasses through a centroid Pw (geometrical center) of the thick portion50 on the face surface, overlaps the thick portion 50, and has a maximumlength. An angle θ1 formed by the central axis line L3 and the toe-heeldirection can be preferably set to 5°≦θ1<90° or more preferably30°≦θ1≦60°, for example.

As shown in FIG. 4, the thick portion 50 includes a face center Pc and asweet spot located in the vicinity thereof, and extends in an “I” shapealong the central axis line L3. Note that the “I” shape in the presentspecification refers to a shape that extends along one straight line.The thick portion 50 of the present embodiment reaches neither the topline L1 nor the sole line L2. Here, the face center Pc is specified asfollows. Specifically, first, in the face portion, a maximum width Wx inthe toe-heel direction is determined, and a central position Px in thetoe-heel direction at the maximum width Wx is determined. Then, at theposition Px, a central point Py in the up-down direction of the faceportion is determined, and this point Py is defined as a face center Pc.Note that FIG. 3 is a cross-sectional view that passes through the facecenter Pc. Also, the sweet spot is the foot of the perpendicular linefrom the center of gravity of the golf club head 100 to the face portion11. Moreover, although the centroid Pw of the thick portion 50 matchesthe face center Pc in the present embodiment, the points Pc and Pw donot need to match. It should be noted that it is preferable that thepoints Pc and Pw are arranged in the vicinity of each other.

In a front view, the thick portion 50 has recessed portions 51 a and 51b on respective sides of the central axis line L3. The recessed portions51 a and 51 b are each a portion formed due to the central region of thethick portion 50 along the central axis line L3 being more recessedtoward the central axis line L3 than the parts of the thick portion 50on the two sides of the central region along the central axis line L3.Here, the recessed portion 51 a is located more toward the heel side,and the recessed portion 51 b is located more toward the toe side. Inthe present embodiment, one such recessed portion is formed on each sideof the central axis line L3. In other words, as shown in FIG. 4, thethick portion 50 of the present embodiment is shaped as an ellipse thatis overall constricted in the central region in the lengthwisedirection, that is to say the central region in the direction of thecentral axis line L3. This constriction is defined by a smooth curvedline, and the thick portion 50 has a peanut shape overall. Also, thethick portion 50 of the present embodiment has a shape that isapproximately line symmetrical with respect to the central axis line L3.Accordingly, the recessed portions 51 a and 51 b are arranged atpositions that oppose each other across the central axis line L3.

Hereinafter, the two intersections where the boundary line L4 betweenthe thick portion 50 and the peripheral portion 60 intersects thecentral axis line L3 will be referred to as points P1 and P2. The pointP1 is the point more toward the toe side (first intersection), and thepoint P2 is the point more toward the heel side (second intersection).Also, the straight line that passes through the point P1 and isorthogonal to the central axis line L3 will be referred to as a straightline L5 (first orthogonal line), and the straight line that passesthrough the point P2 and is orthogonal to the central axis line L3 willbe referred to as a straight line L6 (second orthogonal line).Furthermore, the intersection between the straight line L5 and the topline L1 will be referred to as a point P3, and the intersection betweenthe straight line L6 and the top line L1 will be referred to as a pointP4. Moreover, the intersection between the straight line L5 and the soleline L2 will be referred to as a point P5, and the intersection betweenthe straight line L6 and the sole line L2 will be referred to as a pointP6. Also, the straight line that passes through the face center Fc andis orthogonal to the central axis line L3 will be referred to as astraight line L7.

In general, hit points on the face surface are likely to be distributedalong a straight line that is inclined from the heel side toward the toeside along the direction from the sole side to the top side and.Accordingly, the aforementioned straight line L7 is a hit pointdistribution line along which hit points are approximately distributed.In other words, when a golfer swings a golf club that includes the head100, the points of impact between the ball and the face surface (hitpoints) will be distributed in the vicinity of the straight line L7.Also, the region surrounded by the top line L1, the sole line L2, andthe straight lines L5 and L6 is a hit point distribution region A1 inwhich the hit points are approximately distributed. The hit pointdistribution region A1 has an approximately quadrangular shape with theabove-described points P3 to P6 serving as the four corner points, andin the present embodiment, this region is approximately shaped as aparallelogram.

As described above, the hit point distribution region A1 has the thickportion 50 in the central region in the up-down direction. Accordingly,the face center Fc region is thick, thus ensuring strength for the head100 with respect to impact during ball hitting. Also, the hit pointdistribution line L7 is orthogonal to the central axis line L3 of thethick portion 50 and extends so as to pass through the thick portion 50via the central portion of the thick portion 50, and the recessedportions 51 a and 51 b are located on the hit point distribution lineL7. Accordingly, the thick portion 50 does not occupy a large regionalong the direction of the hit point distribution line L7, and therelatively thinner transition portion 61 and thin portions 62 a and 62 bmainly occupy a large region along the direction of the hit pointdistribution line L7. As a result, the thin high restitution areaspreads out along the actual hit point distribution, the interior of thehit point distribution region A1 flexes easily, and it is possible toimprove the flight-distance. Note that although the straight line L7 isdescribed above as being a hit point distribution line along which hitpoints are approximately distributed, there is no need for theregression line of a large number of actual hit points (referred tohereinafter as the “actual hit point distribution line”) and thestraight line L7 to match. The actual hit point distribution lineextends as indicated by L8 in FIG. 4, and is not necessarily orthogonalto the central axis line L3. However, even in such a case, if the actualhit point distribution line L8 intersects the central axis line L3, theactual hit point distribution line L8 will be approximately containedinside the hit point distribution region A1 that serves as the highrestitution area, and the flight-distance is improved. Note that FIG. 8shows an actual hit point distribution region A2 in which hit points aredistributed when an average golfer makes actual hits. The actual hitpoint distribution region A2 is a region whose central axis is theactual hit point distribution line L8. As can be understood from thisfigure, the majority of the aforementioned hit point distribution regionA1 is overlapped with the actual hit point distribution region A2.

Meanwhile, the transition portion 61 completely surrounds the thickportion 50, and has an approximately uniform width along thecircumferential direction. Also, the transition portion 61 reaches thetop line L1 and the sole line L2, and intersects the top line L1 and thesole line L2 in a line having a length, not in a point. Accordingly, thetransition portion 61 extends over the entire face portion 11 in thetop-sole direction, but is concentrated relatively in the centralportion of the face portion 11 in the toe-heel direction, and reachesneither the heel-side end point Ph nor the toe-side end point Pt. Notethat in the present embodiment, the centroid (geometrical center) of theregion made up of the transition portion 61 and the thick portion 50also approximately matches the face center Pc.

If the thickness of the face portion 11 rapidly decreased in thevicinity of the boundary line between the face portion 11 and the risingportion 12, stress would become concentrated in this thin portion, andthere would be a risk of having an effect on the durability of the faceportion 11. However, in the present embodiment, the transition portion61 is continuous with the top line L1 and the sole line L2 as describedabove. In other words, the thick portion 50 does not suddenly end in thevicinity of the rising portion 12, nor does the thickness of the faceportion 11 rapidly decrease. The strength of the face member 1 istherefore ensured.

Also, as shown in FIG. 4, a V-shaped slit (toe-side groove) 71 that hasthe toe-side end point Pt as its crest and extends along the boundaryline between the face portion 11 and the rising portion 12 is formed onthe inner surface (back surface) of the face portion 11. Similarly, aV-shaped slit (heel-side groove) 72 that has the heel-side end point Phas its crest and extends along the boundary line between the faceportion 11 and the rising portion 12 is formed on the heel side as well.In other words, regions thinner than the thin portions 62 a and 62 b areformed in the vicinity of the toe-side end point Pt and the heel-sideend point Ph. Accordingly, due to these slits 71 and 72, the restitutionfactor can be raised particularly in the toe-side and heel-sideportions, and it is possible to prevent the high restitution area frombeing biased toward the central region on the face surface, and toexpand the high restitution area. As a result, it is possible toincrease the flight-distance even if the ball is not grabbed at thecentral region of the face surface in a mishit or an intentional shot,for example.

In the present embodiment, a thickness w3 of the face portion 11 in theslit 71 is approximately constant, and the relationship w3<w2 issatisfied. Preferably, w3 can be set to 1.0 mm≦w3≦3.0 mm, or morepreferably 1.5 mm≦w3≦2.5 mm, and in the present embodiment, w3=1.70 mm.Similarly, in the present embodiment, a thickness w4 of the face portion11 in the slit 72 is approximately constant, and the relationship w4<w2is satisfied. Preferably, w4 can be set to 1.0 mm≦w4≦3.0 mm, or morepreferably 1.5 mm≦w4≦2.5 mm, and in the present embodiment, w4=w3=1.70mm.

As shown in FIG. 4, the slits 71 and 72 are partially overlapped withthe hit point distribution region A1. The slit 71 on the toe side beginsat the toe-side end point Pt, extends along the top line L1 and arrivesat the corner point P3, and then furthermore extends into the hit pointdistribution region A1 along the top line L1, but does not reach thecorner point P4. Also, the slit 71 begins at the toe-side end point Ptand extends along the sole line L2, but does not reach the corner pointP5. Similarly, the slit 72 on the heel side begins at the heel-side endpoint Ph, extends along the sole line L2 and arrives at the corner pointP6, and then furthermore extends into the hit point distribution regionA1 along the sole line L2, but does not reach the corner point P5. Also,the slit 72 begins at the heel-side end point Ph and extends along thetop line L1, but does not reach the corner point P4.

As described above, in the present embodiment, the slits 71 and 72extend inside the hit point distribution region A1. Accordingly, theinterior of the hit point distribution region A1 can flex more easily,and it is possible to improve the flight-distance.

2. Second Embodiment

Next, a golf club head according to a second embodiment of the presentinvention will be described below with reference to FIG. 5. The head ofthe present embodiment is a utility golf club head, not a driver golfclub head, and has a volume smaller than 400 cubic centimeters. FIG. 5is a front view of a face portion 111 of the head of the presentembodiment in the reference state. Note that it would not actually bepossible to see the thickness structure formed on the inner surface ofthe face portion 111 in FIG. 5, but similarly to the case of FIG. 4, thethickness structure is illustrated in consideration of facilitatingunderstanding.

As can be understood from comparing FIGS. 4 and 5, the head of thepresent embodiment has approximately the same configuration as the head100 of the first embodiment, with mainly the exception that alater-described slit 73 is formed instead of the slits 71 and 72. Forthis reason, the following description focuses on differences from thefirst embodiment, and similar configurations will be denoted by the samereference signs and will not be described.

As shown in FIG. 5, the slit (groove) 73 is formed so as to extend alongthe sole line L2 at a position somewhat biased toward the heel side inthe inner surface (back surface) of the face portion 111 of the presentembodiment. In other words, a region thinner than the thin portions 62 aand 62 b is formed so as to extend along the sole line L2 at a positionsomewhat biased toward the heel side. This slit 73 contributes to animprovement in the restitution factor on the heel-side lower portion inparticular. Specifically, it is possible to prevent the high restitutionarea from being biased toward the central region on the face surface,and to expand the high restitution area toward the heel-side lowerportion. As a result, it is possible to increase the flight-distanceeven if the ball collides with the heel-side lower portion of the facesurface in a mishit or an intentional shot, for example. Note that slitsare not provided at positions along the top line L1 in the presentembodiment. However, unlike the case of a driver, with a utility thereis generally a tendency for the ball hit point to be comparativelybiased toward the lower portion of the face surface. Accordingly, theflight-distance can be effectively extended with merely a slit extendingalong the sole line L2.

In the present embodiment, a thickness w5 of the face portion 111 in theslit 73 is approximately constant, and can be preferably set to 0.8mm≦w5≦2.0 mm, or more preferably 1.0 mm≦w5≦1.5 mm. Also, in the presentembodiment as well, the thickness w1 of the thick portion 50 isapproximately constant, and can be preferably set to 1.5 mm≦w1≦2.5 mm,or more preferably 1.7 mm≦w1≦2.2 mm. Also, the thickness w2 of the thinportions 62 a and 62 b is also approximately constant and can bepreferably set to 1.0 mm≦w2≦2.2 mm, or more preferably 1.4 mm≦w2≦2.0 mm.

The slit 73 is partially overlapped with the hit point distributionregion A1. More specifically, the slit 73 extends so as to pass throughthe entirety of the hit point distribution region A1 along the sole lineL2. The slit 73 extends beyond the corner point P5 toward the toe-sideend point Pt, but does not reach the toe-side end point Pt, andsimilarly extends beyond the corner point P6 toward the heel-side endpoint Ph, but does not reach the heel-side end point Ph. As describedabove, the slit 73 extends inside the hit point distribution region A1,and therefore the interior of the hit point distribution region A1 canflex more easily, and it is possible to improve the flight-distance.

3. Variations

Although several embodiments of the present invention have beendescribed above, the present invention is not limited to theseembodiments, and various modifications can be made without departingfrom the gist of the invention. The following are examples ofmodifications that can be made. The spirits of the following variationscan be combined as appropriate.

3-1

Although the golf club head is a driver or utility type of golf clubhead in the above embodiments, there is no limitation to these types,and it may be a so-called fairway, hybrid, or iron type of golf clubhead, for example. It should be noted that the thickness distributionstructure of the face portion of the present invention can be favorablyapplied to a wood type of golf club head.

3-2

Although the central axis line L3 is inclined relative to the top-soledirection in the above embodiments, it may extend parallel to thetop-sole direction. In other words, the thick portion 50 may extendalong the top-sole direction.

3-3

The shape of the thick portion 50 is not limited to the shapes describedabove. For example, as shown in FIG. 6, it may have a shape in which therecessed portions 51 a and 51 b are defined by an outline that has sharpcorners rather than smooth curves.

Also, as shown in FIG. 7, either the recessed portion 51 a or 51 b canbe omitted. In other words, the recessed portion may be formed on onlyone side of the central axis line.

3-4

In the first embodiment, either the slit 71 or 72 can be omitted. Also,in the second embodiment, a slit may be formed along the top line L1 inaddition to the slit 73.

3-5

The face member 1 does not need to have a cup face structure, and therising portion 12 can be omitted.

REFERENCE SIGNS LIST

1 Face member

11 Face portion

50 Thick portion

51 a, 51 b Recessed portion

60 Peripheral portion

61 Transition portion

62 a, 62 b Thin portion

71-73 Slit (groove)

100, 101 Golf club head

A1 Hit point distribution region

Fc Face center

L1 Top line

L2 Sole line

L3 Central axis line

L4 First orthogonal line

L5 Second orthogonal line

P1 First intersection

P2 Second intersection

P3 First corner point

P4 Second corner point

P5 Third corner point

P6 Fourth corner point

Pt Toe-side end point

Ph Heel-side end point

1. A golf club head comprising a face portion for hitting a ball,wherein the face portion has a thick portion that includes a facecenter, and a peripheral portion that is thinner than the thick portionand surrounds the thick portion, the thick portion extends along acentral axis line that extends in a top-sole direction or in a directioninclined from a toe side toward a heel side along a direction from asole side toward a top side, and the thick portion has a recessedportion on at least one side of the central axis line so that a centralregion of the thick portion along the central axis line is recessed moretoward the central axis line than parts of the thick portion on twosides of the central region along the central axis line.
 2. The golfclub head according to claim 1, wherein the thick portion has therecessed portion on each side of the central axis line.
 3. The golf clubhead according to claim 2, wherein the recessed portions on both sidesof the central axis line oppose each other across the central axis line.4. The golf club head according to claim 1, wherein the central axisline is a line segment having a maximum length among line segments thatpass through a centroid of the thick portion and are overlapped with thethick portion, and intersects a boundary line of the thick portion at afirst intersection and a second intersection, the face portion includesa hit point distribution region, and the hit point distribution regionis surrounded by a first orthogonal line that passes through the firstintersection and is orthogonal to the central axis line, a secondorthogonal line that passes through the second intersection and isorthogonal to the central axis line, and a boundary line of the faceportion, and a groove that extends along the boundary line of the faceportion and is at least partially overlapped with the hit pointdistribution region is formed on a back surface side of the faceportion.
 5. The golf club head according to claim 4, wherein theboundary line of the face portion includes a top line on a top side thatextends between a toe-side end point, being a point farthest on a toeside, and a heel-side end point, being a point farthest on a heel side,and includes a sole line on a sole side that extends between thetoe-side end point and the heel-side end point, the hit pointdistribution region has a first corner point on a toe side and a secondcorner point on a heel side on the top line, and has a third cornerpoint on a toe side and a fourth corner point on a heel side on the soleline, and the groove includes at least one of a toe-side groove and aheel-side groove, the toe-side groove extends at least from the firstcorner point into the hit point distribution region along the boundaryline of the face portion but does not reach the second corner point, andthe heel-side groove extends at least from the fourth corner point intothe hit point distribution region along the boundary line of the faceportion but does not reach the third corner point.
 6. The golf club headaccording to claim 5, wherein the groove includes both the toe-sidegroove and the heel-side groove.
 7. The golf club head according toclaim 5, having a volume of 400 cubic centimeters or more.
 8. The golfclub head according to claim 6, having a volume of 400 cubic centimetersor more.
 9. The golf club head according to claim 4, wherein theboundary line of the face portion includes a sole line on a sole sidethat extends between a toe-side end point, being a point farthest on atoe side, and a heel-side end point, being a point farthest on a heelside, and the groove extends along the sole line.
 10. The golf club headaccording to claim 9, having a volume less than 400 cubic centimeters.11. A golf club head comprising a face portion for hitting a ball,wherein the face portion has a thick portion that includes a face centerand has an approximately uniform thickness, and a peripheral portionthat is thinner than the thick portion and surrounds the thick portion,the thick portion extends along a central axis line that extends in adirection from toe-down to heel-up, the central axis line is a linesegment having a maximum length among line segments that pass through acentroid of the thick portion and are overlapped with the thick portion,and the thick portion has a recessed portion on at least one side of thecentral axis line so that a central region of the thick portion alongthe central axis line is recessed more toward the central axis line thanparts of the thick portion on two sides of the central region along thecentral axis line, thus approximately forming a shape as obtained byproviding an ellipse whose long axis extends substantially along thecentral axis line with the recessed portion.
 12. The golf club headaccording to claim 11, wherein the thick portion does not reach theboundary line of the face portion on both the top side and the soleside.
 13. The golf club head according to claim 11, wherein an angle θ1formed by the central axis line and a horizontal direction satisfies acondition θ1<60°.
 14. The golf club head according to claim 12, whereinan angle θ1 formed by the central axis line and a horizontal directionsatisfies a condition θ1<60°.
 15. The golf club head according to claim11, wherein the ellipse has a shape that is approximately linesymmetrical with respect to the central axis line.
 16. The golf clubhead according to claim 12, wherein the ellipse has a shape that isapproximately line symmetrical with respect to the central axis line.17. The golf club head according to claim 13, wherein the ellipse has ashape that is approximately line symmetrical with respect to the centralaxis line.
 18. The golf club head according to claim 14, wherein theellipse has a shape that is approximately line symmetrical with respectto the central axis line.
 19. A golf club head comprising a face portionfor hitting a ball, wherein the face portion has a thick portion thatincludes a face center and has an approximately uniform thickness, and aperipheral portion that is thinner than the thick portion and surroundsthe thick portion, the thick portion extends along a central axis linethat extends in a top-sole direction that is a vertical direction, thecentral axis line is a line segment having a maximum length among linesegments that pass through a centroid of the thick portion and areoverlapped with the thick portion, and the thick portion has a recessedportion on at least one side of the central axis line so that a centralregion of the thick portion along the central axis line is recessed moretoward the central axis line than parts of the thick portion on twosides of the central region along the central axis line, thusapproximately forming a shape as obtained by providing an ellipse whoselong axis extends substantially along the central axis line with therecessed portion.